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Question

Difficulty: MediumSpeed and Road Conditions

A commercial motor vehicle is traveling along a rural two-lane highway where the posted speed limit is 50 mph. As weather conditions deteriorate and packed snow covers the roadway, which combination of speed adjustment and control configuration is required for safe operation?

  1. A
    Reduce speed by only 5 mph since perception distance remains unchanged on winter road surfaces.
  2. Reduce speed to 25 mph or lower and ensure the engine retarder is turned off.Answer
  3. C
    Reduce speed to 25 mph and switch the engine retarder to its highest setting to assist the drive wheels.
  4. D
    Maintain normal highway speed on straight sections and apply firm, continuous braking while navigating curves.

Answer

Reduce speed to 25 mph or lower and ensure the engine retarder is turned off.
According to official commercial driving standards, operating on packed snow requires reducing road speed by at least one-half (from 50 mph down to 25 mph or less) and turning off all engine retarder systems to prevent drive-wheel skids.

Step-by-Step Solution

1
Determine the required CDL speed reduction rule for packed snow.
On packed snow, commercial drivers must reduce vehicle speed by at least half (50% or more) from the normal dry-road operating speed.
Traction is severely diminished on packed snow, drastically increasing stopping distance.
2
Apply the speed calculation to the 50 mph baseline speed.
50 mph reduced by half yields a maximum safe speed of 25 mph.
Matching vehicle speed to available traction prevents losing directional control.
3
Assess the auxiliary braking and retarder requirements for slippery surfaces.
Engine retarders must be disabled on snow, ice, or wet pavement.
Retarder braking force is applied exclusively to the drive wheels and can easily exceed available friction, locking the wheels and causing a jackknife or skid.

Key Concept

Speed reduction standards and retarder safety protocol for packed snow conditions
Estimated Time:1m 0s
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Topics

Speed and Road Conditions

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